For any weak acid indicator (Hln) colour change is observed when

Options

A. `([ln^(-)])/([Hln])=(1)/(10)`
B. `pH=pK_(a)-1`
C. Both (A ) and (B)
D. None of these

Answer

C

Explanation

`Hln hArr H^(+)+ln^(-)`
`pH =pK_(a)+log.([ln^(-)])/([Hln])`
When colour of the unionized form is seen
`([ln^(-)])/([Hln])=(1)/(10):. pH =pK_(a)-1`